/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformMisc.h
Note: This is NOT a user or machine fingerprint, as multiple logins on the same machine will not share the same ID, and it is not based on the hardware of the user. It is completely random and non-identifiable.
a string containing the LoginID, or empty if not available.
static [FString](API\Runtime\Core\Containers\FString) GetLoginId()